/*返回顶部*/
function toUp(className){
	if($(window).scrollTop()>$(window).height()){
    	$('.'+className).fadeIn(300);
    }else{
    	$('.'+className).fadeOut(300);
    }
}
function goUpAnimate(className){
	$('html,body').animate({scrollTop: '0px'}, 300);
}
$(function() {
toUp("top_a");
  $(window).scroll(function() {
    toUp("top_a");
});
  });